﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace CSharpExt.Util
{
    public class Crc16
    {
        public UInt16 Value
        {
            get
            {
                return m_wCrc;
            }
        }

        private UInt16 m_wCrc = 0;

        private static int[] crctab = {
		0x0, 0xc0c1, 0xc181, 0x140, 0xc301, 0x3c0, 
		0x280, 0xc241, 
		0xc601, 0x6c0, 0x780, 0xc741, 0x500, 0xc5c1, 
		0xc481, 0x440, 
		0xcc01, 0xcc0, 0xd80, 0xcd41, 0xf00, 0xcfc1, 
		0xce81, 0xe40, 
		0xa00, 0xcac1, 0xcb81, 0xb40, 0xc901, 0x9c0, 
		0x880, 0xc841, 
		0xd801, 0x18c0, 0x1980, 0xd941, 0x1b00, 0xdbc1, 
		0xda81, 0x1a40, 
		0x1e00, 0xdec1, 0xdf81, 0x1f40, 0xdd01, 0x1dc0, 
		0x1c80, 0xdc41, 
		0x1400, 0xd4c1, 0xd581, 0x1540, 0xd701, 0x17c0, 
		0x1680, 0xd641, 
		0xd201, 0x12c0, 0x1380, 0xd341, 0x1100, 0xd1c1, 
		0xd081, 0x1040, 
		0xf001, 0x30c0, 0x3180, 0xf141, 0x3300, 0xf3c1, 
		0xf281, 0x3240, 
		0x3600, 0xf6c1, 0xf781, 0x3740, 0xf501, 0x35c0, 
		0x3480, 0xf441, 
		0x3c00, 0xfcc1, 0xfd81, 0x3d40, 0xff01, 0x3fc0, 
		0x3e80, 0xfe41, 
		0xfa01, 0x3ac0, 0x3b80, 0xfb41, 0x3900, 0xf9c1, 
		0xf881, 0x3840, 
		0x2800, 0xe8c1, 0xe981, 0x2940, 0xeb01, 0x2bc0, 
		0x2a80, 0xea41, 
		0xee01, 0x2ec0, 0x2f80, 0xef41, 0x2d00, 0xedc1, 
		0xec81, 0x2c40, 
		0xe401, 0x24c0, 0x2580, 0xe541, 0x2700, 0xe7c1, 
		0xe681, 0x2640, 
		0x2200, 0xe2c1, 0xe381, 0x2340, 0xe101, 0x21c0, 
		0x2080, 0xe041, 
		0xa001, 0x60c0, 0x6180, 0xa141, 0x6300, 0xa3c1, 
		0xa281, 0x6240, 
		0x6600, 0xa6c1, 0xa781, 0x6740, 0xa501, 0x65c0, 
		0x6480, 0xa441, 
		0x6c00, 0xacc1, 0xad81, 0x6d40, 0xaf01, 0x6fc0, 
		0x6e80, 0xae41, 
		0xaa01, 0x6ac0, 0x6b80, 0xab41, 0x6900, 0xa9c1, 
		0xa881, 0x6840, 
		0x7800, 0xb8c1, 0xb981, 0x7940, 0xbb01, 0x7bc0, 
		0x7a80, 0xba41, 
		0xbe01, 0x7ec0, 0x7f80, 0xbf41, 0x7d00, 0xbdc1, 
		0xbc81, 0x7c40, 
		0xb401, 0x74c0, 0x7580, 0xb541, 0x7700, 0xb7c1, 
		0xb681, 0x7640, 
		0x7200, 0xb2c1, 0xb381, 0x7340, 0xb101, 0x71c0, 
		0x7080, 0xb041, 
		0x5000, 0x90c1, 0x9181, 0x5140, 0x9301, 0x53c0, 
		0x5280, 0x9241, 
		0x9601, 0x56c0, 0x5780, 0x9741, 0x5500, 0x95c1, 
		0x9481, 0x5440, 
		0x9c01, 0x5cc0, 0x5d80, 0x9d41, 0x5f00, 0x9fc1, 
		0x9e81, 0x5e40, 
		0x5a00, 0x9ac1, 0x9b81, 0x5b40, 0x9901, 0x59c0, 
		0x5880, 0x9841, 
		0x8801, 0x48c0, 0x4980, 0x8941, 0x4b00, 0x8bc1, 
		0x8a81, 0x4a40, 
		0x4e00, 0x8ec1, 0x8f81, 0x4f40, 0x8d01, 0x4dc0, 
		0x4c80, 0x8c41, 
		0x4400, 0x84c1, 0x8581, 0x4540, 0x8701, 0x47c0, 
		0x4680, 0x8641, 
		0x8201, 0x42c0, 0x4380, 0x8341, 0x4100, 0x81c1, 
		0x8081, 0x4040
		};

        public Crc16()
        {
            Reset();
        }

        public void Reset()
        {
            m_wCrc = 0;
        }

        public void Update(byte[] bBuff, int iOffset, int iCnt)
        {
            UInt16 index;
            int iPositionCounter = iOffset;

            while (Convert.ToBoolean(iCnt--))
            {
                index = (UInt16)(((m_wCrc ^ (UInt16)bBuff[iPositionCounter]) & 0xff));
                m_wCrc = (UInt16)(((m_wCrc >> 8) & 0xff) ^ crctab[index]);

                iPositionCounter++;
            }
        }

    }
}
